With the ever increasing demands from networked society, either on huge traffic volume or very low latency or both, mobile networking needs to continuously evolve to fulfil the requirements. For example, the Next Generation Mobile Networks Alliance defines requirements for 5G networks (5th generation mobile networks or 5th generation wireless systems) which are new networks surpassing current 4G at least in terms of data rate, number of simultaneous connections and spectral efficiency.
Some consensus is reached about how to meet the requirements for the next generation of 3GPP systems, i.e. 5G systems. A first proposal is to densify the network, and a second proposal is to use more spectrum. Due to scarcity of the so far used, typically most attractive spectrum ranges, the bulk of the available frequencies for next generation (5G) networks that are practically usable may be located in very high frequency ranges, compared to the frequencies that have so far been used for wireless communication, such as 10 GHz and above.
For such high frequency spectrum, the atmospheric attenuation, penetration and diffraction properties are much worse than for the lower frequency spectrum. In addition, the receiver antenna aperture, as a metric describing the effective receiver antenna area that collects the electromagnetic energy from an incoming electromagnetic wave, is frequency dependent, i.e., the link budget would be worse for the same link distance even in a free space scenario, if omnidirectional receive and transmit antennas are used. This motivates the usage of beamforming to concentrate the energy to compensate for the loss of link budget in the high frequency spectrum.
In addition to the usage of beamforming, reducing energy consumption in radio networks is an overall design criterion for 5G systems. As exemplary background, the IEEE paper of the IEEE 25th Annual International Symposium on Personal, Indoor, and Mobile Radio Communication (PIMRC), 2-5 Sep. 2014, Washington, D.C., USA, pp. 1300-1304 “A Clean Slate Radio Network Designed for Maximum Energy Performance” by Pal Frenger, Magnus Olsson, and Erik Eriksson (ISBN 978-1-4799-4912-0) proposes a clean slate radio network system that has been designed with the aim to maximize energy performance and assumes a logical separation between idle mode network functionality and user plane data transmission and reception.
In particular, some of the previous research in this area considers as a design goal the minimization of the amount of “always-on” signals, such as synchronization signals, e.g. the primary synchronization signal (PSS) and the secondary synchronization signal (SSS), the cell-specific reference signals (C-RS) and the broadcasted system information in the 4G (LTE) system. In general, it is proposed to minimize the amount of information over the air interface not directly associated with the transmission of data. This requirement may lead to challenges associated with system access, specifically for 5G, because these “always-on” signals are so called common signals/channels used for system access procedures. For example, in LTE a UE (User Equipment) needs to detect PSS/SSS in order to camp on a cell and get time and frequency synchronization before it can receive C-RSs, perform channel estimation and read system information. In order to be capable of accessing the system when coming from idle mode, the UE needs to acquire the RACH configuration from SIB2 (system information block 2). In summary, minimizing always-on signals should be carefully considered in the design of system access procedures.
When, for example, considering the new 5G system, the usage of beamforming and the aimed minimization of always-on transmissions will lead to new problems especially in the case the UE needs to rely on common signals typically always on (contradicting the energy efficiency requirements) and broadcasted (challenging to be realized in a beamforming-based system). The evolvement in transmission of reference signals today to not “always on” reference signals in an ultra-lean system as well as minimization of broadcasted system information is outlined in FIG. 1. This ultra-lean design drives the minimization of always-on signals.
Mobile communication systems are known to have different operation states and usually have some kind of energy saving state, often also referred to as “idle state” or “dormant state”, where the UE procedures are optimized to reduce the UE's energy consumption.
To achieve that goal and at the same time enable that the UE in the energy saving state can still be reached by the network, the UE can move around within a defined coverage area, e.g. a multi-cell area defined by a tracking area list in LTE, without informing the network of its whereabouts. The UE still needs to listen for transmissions from the network in this state, in order to measure the signal quality, perform cell re-selection, when needed, read system information, monitor paging channels and send location area updates so that it can be reached by the network. The network provides the signals for the UE to measure on (as well as the system information) through continuously and often frequently repeated broadcasted transmissions. In the case of LTE, the energy saving state optimized for UE battery savings is the RRC_IDLE/ECM_IDLE state. In that state the UE basically listens to PSSs/SSSs that encode the physical cell identity (PCI), enabling the UE to detect the cell, perform cell reselection (without the need to report to the network) and read the system information to detect whether tracking area updates are needed. Based on the PCI the UE can derive the cell-specific reference signal (C-RS) configuration and perform channel estimation in order to decode the system information.
It is desirable that new systems, such as 5G systems, also comprise some kind of energy saving state(s), which for instance could be denoted “idle” and/or “dormant”, wherein the UE should remain most of the time in a low-power, energy efficient mode by reducing the amount of measurements to be performed, channels to be monitored and reports to be sent to the network, A generic state with at least some of these or similar properties is herein referred to as “energy saving state”. Surely, even if the system does not require a UE to enter into a specifically defined energy saving state, resources, such as battery power, may be saved, if the amount of signaling can be reduced in an active state or other similar operation state.
The above described desire for an energy saving UE state may have conflicting requirements with the assumption that a 5G system will have mostly dedicated transmissions (i.e. UE-specific) and activated on a per-need basis or on-demand basis to fulfil requirements on energy efficiency.
If in addition to the lean design principle addressed-above beamforming is also desired so that additional challenges may exist. As beamforming is used to concentrate the energy to enable and/or improve communication between an Access Node (AN) and a UE, a beam preferably has to be targeting a single UE at a time. Such UE specific beams are preferably activated on a per-need basis (according to the lean design principle), but a possible alternative may be to have a set of fixed beams more or less always active. The UE specific beams rely on frequent feedback from the UE to support the adaptation or replacement of the beam to follow the UE's movements. Such frequent feedback counteracts the purpose of the energy saving state to save energy and battery charge in the UE.
In addition, maintaining such beams for a significant number of UEs in an energy saving state is demanding for the network and may consume a significant amount of its capacity, especially in the case of systems with limited beamforming capability, such as systems using analog beamforming. On the other hand, continuous frequently repeated transmissions to support UEs in energy saving state in the manner of legacy systems counteract the requirement, e.g. in 5G networks, to be energy efficient.
It is thus desirable to provide methods, an access node, user equipment, a system and a computer program to enhance resource and energy efficiency in a network and particularly in a UE.